The present commercial method for manufacturing organohalosilanes is well known and is described in U.S. Pat. No. 2,380,995-Rochow. Rochow discloses the direct reaction of an organohalide such as methylchloride with silicon particles in order to produce organochlorosilane. Intermixed with such particles of silicon are particles of copper, thereby forming a reactive mass. In commercial practice this reaction is generally carried out in one of three types of equipment: the stirred bed type of reactor as described in Sellers U.S. Pat. No. 2,449,821, the fluidized bed reactor described in Reed, et al. U.S. Pat. No. 2,389,931, or the rotary kiln.
Organotrichlorosilanes and diorganodichlorosilanes are the two basic products of the above described "direct process" reaction. Such compounds are utilized in the production of organopolysiloxane resins as described in U.S. Pat. Nos. 2,258,218 through 2,258,222. Other products include organopolysiloxane fluids as described in U.S. Pat. No. 2,469,888 and U.S. Pat. No. 2,469,890 as well as the organopolysiloxane elastomers described in U.S. Pat. No. 2,448,756. These patents are generally considered to be the pioneers in the polysiloxane area. Since that time the silicone industry has experienced substantial innovation in this field and a substantial patent literature has evolved relating to the different types of compositions that can be produced from basic organochlorosilanes. It is preferable to produce the diorganodichlorosilanes in a high production manner since they can be utilized most widely, particularly in producing the linear polysiloxane fluids and polymers used in the production of heat cured rubber elastomers and room temperature vulcanizable silicone rubber compositions of various types.
There have been numerous improvements to the direct process for producing alkylhalosilanes as described above. Of particular interest is a method disclosed in copending patent applications of Shah and Ritzer Ser. No. 193,761 filed Oct. 3, 1980, and Ser. No. 209,635 filed Nov. 24, 1980, which are hereby incorporated by reference. These patent applications describe a method for classifying by particle size the residual silicon powder contact mass from the fluidized reactor bed thereby enabling the recycling of substantial amounts of relatively pure silicon powder at a great cost savings.
Although the present invention can be useful in the manufacture of many organohalosilanes, the present disclosure is particularly related to a process for the manufacture of methylchlorosilanes by reacting metallurgical grade silicon with methylchloride at 250.degree. to 350.degree. C. in the presence of copper, followed by condensation and separation of methylchlorosilanes from the crude reaction product mixture.
The gaseous mixture of methylchlorosilanes and unreacted methylchloride will entrain particles of residual contact mass powder from the fluid bed reactor. The gaseous mixture passes through a series of cyclones where most of the powder is separated from the gaseous crude. Such cyclones are never one hundred percent efficient and there is always some residual powder left in the gaseous crude after it leaves the last cyclone. This powder must be removed from the gaseous crude before condensation. If condensation is carried out before removing this powder, the inside surfaces of the condensers will become encrusted with the silicon and copper powder and will become clogged as the condenser passages become obstructed. Furthermore, the downstream separation unit will also become encrusted and plugged in a similar manner. Consequently, after a short running time, the system has to be stopped, opened up and cleaned out. One way of removing the fine powder is to use a scrubber-revaporizer system. With such a system, the powder-laden gas crude flows countercurrent to a stream of liquid chlorosilanes in a scrubbing tower with sieve plates. The liquid flows down from the top and entrains the powder in slurry form which flows out of the scrubber into a vessel called the revaporizer. The scrubbed gaseous crude then flows out of the scrubber from the top and is condensed. The relatively dilute slurry may be concentrated in the revaporizer by heating and constantly agitating the slurry. This is a necessary procedure because of the valuable chlorosilanes contained in the slurry. The vapors formed in the revaporizer are passed back into the scrubber. The concentrated slurry in the revaporizer may be disposed by incineration. This method of removing powder from gaseous crude has a particular disadvantage in that it leads to the loss of fine silicon and copper powder from the slurry as well as the loss of some chlorosilanes. Additionally, there is significant energy consumption in the revaporizer and the incinerator. It was therefore felt that considerable savings could be accomplished if some or all of these disadvantages could be avoided. Furthermore, the use of a revaporizer is a relatively difficult operation because of the mixing requirement and the need to transfer the thick slurry and the agitator seals on such equipment require periodic and costly maintenance. Furthermore, not only is the transport of the thick slurry often a difficult operation, at times the slurry will set like hard cement requiring costly shutdown in order to dig out the hard crust.
It is therefore an object of the present invention to provide a process for removing the residual powder from the gaseous crude of organohalosilanes from a direct process fluidized reactor bed.
It is a further object to provide a process for removing residual silicon and copper powder in a less costly and burdensome manner than heretofore available.
It is another object to eliminate the necessity of a scrubber-vaporizer in a direct process organohalosilane system.
It is another object of the present invention to provide relatively pure gaseous organohalosilane mixtures which do not contain residual reactor mass fines.
These and other objects will become apparent to those skilled in the art upon consideration of the following specification, claims and accompanying drawings.